Music

All games should have some kind of music, and it should be optional. If you don't have any, get some free loops from flashkit.com. Once you add music it is much more fun because your brain has something to do when there is a lapse in the action.

Another thing is to use those loops in an ingame music mixer or dynamically generating music. Stereo panning is another good thing to add. Music shouldn't be too loud either, esp. if you have voiceovers/speaking characters or sounds that must be heard.

I think one thing that works well is type of music which changes based on the state of the game. For example, play 'soothing' music while out looking for trees to cut down. Play more suspensefull music while trying to dodge environmentalists who don't see the point for you to build yet another forge for your army.

I myself like to create tiny small loops. By themselves, they get quickly annoying. But my idea is that other sounds will be layered over the bottom rythm (spell?) track which contains mostly a beat. Perhaps mixing in some synths and what not.

One thing I would like to see is (and now that we have faster CPUs, we can do this) is more real-time filtering of music and sound in a game. Take one sound, run it through some filters (or one) and produce an alternative to the basic sound. This would allow for a much wider variety of sounds without needing 10 dics of game assets.

Like adding echos for sounds if you are inside an interior. Basing those echos on the size of the room, and perhaps the acoustic characteristics. This would really immerse the player.

Another thing which I don't notice much. One walking/running, many games you the same footstep sounds. But as a player moves from a carpeted room, to a metal floor room, to the outside with snow, the footstep sounds should be different. Same goes for motion. Build up speed and step will come more often. Many games you the same sound for whatever speed the player is running at. (BTW, I don't play many state-of-the-art games, so perhaps new AAA games do all this.)

Other thing about sound is having a nice sound/music for your logo's intro. I like to think the start of a game as the same as a movie, ie 20th Century Fox drum roll, SKG Dreamworks piano/guitar. A signature "whoooosh" or sound jingle is very good IMHO. Good to set branding.